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In the lands between
the Arctic Circle and the tropics,
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00:00:50,480 --> 00:00:54,120
each year brings a great change
between winter and summer,
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00:00:54,280 --> 00:00:59,000
imposing a rhythm
in the lives of animals and plants.
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00:00:59,160 --> 00:01:02,120
Up north in the great evergreen forests,
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00:01:02,280 --> 00:01:05,400
conditions in mid-winter are cripplingly severe.
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00:01:12,680 --> 00:01:15,640
Life, if it is to flourish, has three needs:
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Light, warmth and moisture.
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00:01:19,440 --> 00:01:23,760
And the reason trees like these
don't grow much farther north
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00:01:23,920 --> 00:01:26,200
is not only the extreme cold,
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but with the long months of winter darkness,
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there is not enough light in the year
for them to grow.
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00:01:33,800 --> 00:01:38,960
Here in northern Norway,
300 miles, 500km north of the Arctic Circle,
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00:01:39,120 --> 00:01:43,120
there is just enough light,
but it does get extremely cold.
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70 degrees of frost
have been measured here,
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and in winter there are very heavy snowfalls.
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The cold threatens to freeze
the liquid within the trees,
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and denies them
one of their essential supplies: Water.
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Although snow and ice lie all around,
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the trees can't tap that water while it's frozen.
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So this land is effectively as parched as a desert,
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and the pine trees have as great a need
to conserve water as a cactus.
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All plants lose some water through their leaves,
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but pine needles are protected
by a near-impermeable rind.
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The pores through which they breathe,
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and from which water can evaporate,
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are kept out of the wind by being placed
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along the groove
that runs the length of the needle,
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each in a tiny pit ringed with a ridge.
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These dry, waxy leaves are almost inedible,
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but the seeds in the cones are not,
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and are one of the few kinds of food
available in the forest in winter.
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The crossbill's special beak
enables it to separate the cone's segments
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and prise out the nutritious seeds.
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This winter feast is never certain.
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00:03:16,560 --> 00:03:20,560
Some years every branch of the trees
will be laden with cones,
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in others there will only be a handful.
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Then the seed-eaters must move on or die.
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The few remaining cones
can then shed their seeds into the snow
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when there are few animals around.
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00:03:39,920 --> 00:03:42,200
Even so, there "are" some.
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Voles make their runways
through the snow and collect what they can.
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Moose get little nourishment from pine trees,
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apart from the shaggy moss
that hangs from the branches.
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00:04:13,600 --> 00:04:16,960
They chew the sappy twigs and bark of birch,
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but there's not enough to keep them going.
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00:04:21,720 --> 00:04:27,440
If it wasn't for the fat reserves
they built up in summer, few would survive.
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00:04:31,120 --> 00:04:34,800
The winter forests
can support very few plant-eaters,
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00:04:34,960 --> 00:04:39,680
but there are just enough
to feed one or two hardy hunters.
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00:04:57,640 --> 00:05:02,240
The great grey owl's legs
are ideal for grabbing prey in snow:
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Long and covered with warm feathers.
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It regularly patrols the snow,
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for it can't afford to miss
a single opportunity of a meal.
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And this is an incautious move.
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Lynx seek bigger prey.
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The female has young, which, though large,
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are not yet skilled enough
to hunt for themselves, so they rely on her.
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The cost-efficiency of hunting
is precisely calculated.
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00:06:52,880 --> 00:06:56,440
If the lynx doesn't catch a hare within 200 yards,
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the meat it might provide
is not enough to warrant the effort,
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00:07:01,520 --> 00:07:04,400
and the lynx gives up.
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00:07:07,800 --> 00:07:11,200
Bigger prey are worth much longer chases,
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00:07:11,360 --> 00:07:16,080
and the lynx pursue roe deer
with great persistence.
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00:07:26,120 --> 00:07:31,280
A single deer will provide food
for the whole lynx family.
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In this bleak land,
even the most ferocious and capable hunters
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do not scorn to scavenge.
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An eagle owl will take cold deer flesh
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just as eagerly as the warm bodies of voles.
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00:08:00,040 --> 00:08:03,440
A wolverine, the biggest of the weasel family,
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and more than a match for an eagle owl.
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00:08:43,360 --> 00:08:46,960
The coniferous forest grows right round the globe
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in a belt that, in places, is 1,200 miles across.
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From Scandinavia, it extends
across northern Europe and Siberia
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to the shores of the Pacific.
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00:09:01,720 --> 00:09:05,240
During the last ice age,
when the seas were lower,
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the Bering Strait did not exist,
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so the trees continued into North America,
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across northern Canada to the Atlantic.
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Consequently,
all the trees in this vast forest
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and its permanent inhabitants
in America, Asia and Europe, are much the same.
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00:09:28,080 --> 00:09:32,560
But when spring comes,
visitors journey up from warmer parts
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and each forest
takes on its own individual character.
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In Scandinavia, a hawk owl,
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a nomad that has spent the winter
farther south,
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comes cruising up north again
looking for food and a nest site.
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00:09:56,040 --> 00:09:59,640
Unlike other owls,
it's primarily a daytime hunter,
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00:09:59,800 --> 00:10:04,560
and relies not so much
on its acute hearing as its sharp eyesight
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00:10:04,720 --> 00:10:08,520
as it waits for the melting snow
to reveal rodents.
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00:10:36,400 --> 00:10:38,960
In pine trees, from Norway to Siberia,
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the cock capercaillie claims his territory.
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This giant grouse is one of the few creatures
that eats pine needles.
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His hen takes them too.
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00:11:07,000 --> 00:11:09,280
Now is the time for nesting.
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00:11:09,440 --> 00:11:12,040
The hawk owl is in search of a hole in a tree,
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00:11:12,200 --> 00:11:14,440
for it's already found its partner.
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00:11:16,720 --> 00:11:19,640
But many tree holes are occupied,
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00:11:19,800 --> 00:11:25,520
for great numbers of owls
have travelled up to feed on the voles.
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00:11:28,400 --> 00:11:31,120
No owl can dig a hole for itself.
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00:11:31,280 --> 00:11:35,760
They rely mainly on woodpeckers,
and none is a more expert carpenter
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00:11:35,920 --> 00:11:39,320
than the black woodpecker of northern Europe.
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00:11:39,480 --> 00:11:43,560
Their sharp beak serves as an excellent chisel,
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but most prefer to work in dead trees
where the wood is softer.
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There are ants near this tree too,
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which the woodpeckers rely on for food in winter.
104
00:12:08,920 --> 00:12:11,080
Not all owls use nest holes.
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00:12:11,280 --> 00:12:14,680
The eagle owl nests on the ground, among rocks.
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It already has a clutch of three eggs,
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00:12:18,760 --> 00:12:23,120
for, being a permanent resident
of these forests, it paired early.
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00:12:32,440 --> 00:12:35,280
Plants now have their chance to breed.
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The wood anemones
are already in flower, as are the pines.
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00:12:39,280 --> 00:12:42,040
Each tree produces male and female flowers,
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which mature at different times,
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so the female flowers are likely
to be fertilised by pollen from other trees.
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00:12:52,080 --> 00:12:55,640
Now it is as warm as it ever will be
in the northern forests.
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Summer visitors are arriving,
and the trees echo with their song.
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(BIRDSONG AND INSECTS BUZZING)
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00:13:05,680 --> 00:13:09,320
This willow warbler,
singing so vigorously in Scandinavia,
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00:13:09,480 --> 00:13:12,880
has come all the way from the savannah country
south of the Sahara.
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00:13:13,040 --> 00:13:15,960
So has the winchat.
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00:13:16,920 --> 00:13:19,800
And the lure that has brought them so far
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00:13:19,960 --> 00:13:23,560
is the sudden emergence of myriads of insects.
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00:13:32,720 --> 00:13:37,760
This bedraggled creature is hardly recognisable,
for its wings have not yet expanded.
122
00:13:37,920 --> 00:13:40,080
It's a pine beauty moth,
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00:13:40,240 --> 00:13:44,120
and its first priority is to leave the forest floor
which is full of danger.
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00:13:44,280 --> 00:13:47,640
But not all the moths have such a clear run.
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00:13:52,720 --> 00:13:55,680
Shrews are among the first to feed on them.
126
00:13:57,680 --> 00:14:01,760
Up among the pine needles,
the pine beauty pumps fluid out of its body
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00:14:01,920 --> 00:14:04,160
and into the veins of its wings.
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00:14:12,920 --> 00:14:17,560
Here the moths will lay their eggs
so their caterpillars can feed on the young shoots.
129
00:14:19,000 --> 00:14:21,360
The wood ants have missed their chance
to catch the adult moth,
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00:14:21,520 --> 00:14:25,160
but now they're looking for the caterpillars
among the branches.
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00:14:27,200 --> 00:14:31,080
The colour and the pattern of the caterpillar
conceals it from birds which hunt by sight,
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00:14:31,240 --> 00:14:36,280
but is no protection
against ants which search by smell and touch.
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00:15:03,480 --> 00:15:08,320
Finally the body is hauled down to the nest
for all to consume.
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00:15:14,560 --> 00:15:18,760
The caterpillars of the sawfly
are also swarming on the pine shoots.
135
00:15:18,920 --> 00:15:22,320
They do have a defence against ants:
A chemical one.
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00:15:22,480 --> 00:15:28,000
As they chew, they store some of the resin from
the pine needles in a pouch inside their mouth.
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00:15:28,160 --> 00:15:34,320
When a foraging ant discovers them,
they dab a spot of this resin on its head, like this.
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00:15:36,240 --> 00:15:45,040
The resin damages the ant's eyes and antennae,
so disorientating it that it can hardly walk.
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00:15:45,200 --> 00:15:47,520
Even if it finds its way back to the nest,
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00:15:47,680 --> 00:15:54,000
it smells so strongly and strangely that
the other ants treat it as an intruder and kill it.
141
00:15:59,280 --> 00:16:01,840
The ants themselves are food for others.
142
00:16:04,120 --> 00:16:08,400
The wryneck is a member of the woodpecker
family that has specialised in eating ants,
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00:16:08,560 --> 00:16:11,840
and particularly relishes their cocoons.
144
00:16:15,120 --> 00:16:21,760
Like its cousins, the wryneck nests in holes
in trees, but it doesn't excavate them for itself.
145
00:16:21,920 --> 00:16:26,680
It is yet another tenant
of vacated woodpecker holes.
146
00:16:35,800 --> 00:16:41,440
With a long tongue you can even collect insects
from the bark without leaving your nest.
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00:16:43,400 --> 00:16:46,000
Here in the far north, close to the Arctic Circle,
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00:16:46,160 --> 00:16:52,280
the sun during the summer hardly sinks
below the horizon and the nights are brief.
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00:16:57,240 --> 00:17:01,760
The eagle owl hunts just as effectively
in the twilight as in the dark.
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00:17:01,920 --> 00:17:07,400
It has a rabbit. The season is a good one
and game is abundant.
151
00:17:08,560 --> 00:17:12,120
Down in the nest on the forest floor,
there is only one chick left.
152
00:17:12,280 --> 00:17:15,800
The other two may have been taken by foxes.
153
00:17:19,520 --> 00:17:24,000
Eagle owls often kill rival species,
and this chick's last meal was a short-eared owl,
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which it's not yet finished.
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00:17:27,560 --> 00:17:30,120
The single survivor
has a superabundance of food.
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00:17:30,280 --> 00:17:36,000
It has grown fast and its adult feathers
are already appearing through its down.
157
00:17:36,160 --> 00:17:39,600
The tail of a red squirrel
is left over from a previous meal,
158
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and it even takes that too.
159
00:17:55,840 --> 00:17:58,320
The voles are swarming on the forest floor.
160
00:17:58,480 --> 00:18:01,760
Last winter, the pines produced
great quantities of seed,
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00:18:01,920 --> 00:18:04,240
so many adult voles survived till spring
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00:18:04,400 --> 00:18:07,680
and now they're all breeding
at an extraordinary rate.
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00:18:07,840 --> 00:18:11,000
This female produced her four young
only three weeks ago,
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00:18:11,160 --> 00:18:17,600
but she is already pregnant again and will soon
abandon this family and start a new one.
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00:18:43,120 --> 00:18:46,200
All the owls, some visitors, some residents,
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00:18:46,360 --> 00:18:49,480
scour the forest for voles.
167
00:18:57,760 --> 00:19:04,800
Tengmalm's owl, up in a tree hole, has three
chicks, all flourishing and all demanding voles.
168
00:19:33,920 --> 00:19:36,280
The number of voles varies considerably.
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00:19:36,440 --> 00:19:39,800
It gradually builds up
over a period of five to six years
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until finally there are so many that they eat out
their food supply and the population crashes.
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00:19:46,240 --> 00:19:49,160
These changes have their effect
on the owl population.
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00:19:49,320 --> 00:19:51,920
More voles mean better-fed owls,
173
00:19:52,080 --> 00:19:55,000
which produce bigger clutches of eggs
and rear more chicks.
174
00:19:55,160 --> 00:20:00,280
And as the number of owls increases,
so they spread out into new territory.
175
00:20:00,440 --> 00:20:04,240
I'm in Finland, very close to the Russian border.
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00:20:04,400 --> 00:20:09,000
In fact, those pine forests behind me
are actually in Russia.
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00:20:09,160 --> 00:20:13,960
But the frontier is no barrier to the bird
they call the phantom of the north,
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00:20:14,120 --> 00:20:16,040
the great grey owl,
179
00:20:16,200 --> 00:20:19,040
and in years when the vole population is high,
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00:20:19,200 --> 00:20:24,920
the owl comes across these frontiers
and into the Finnish pine forests.
181
00:20:25,080 --> 00:20:28,720
And I know they are here already
because I have just picked up this.
182
00:20:28,880 --> 00:20:30,960
This is an owl pellet.
183
00:20:31,120 --> 00:20:37,800
All owls, as part of their natural digestion,
throw up the fur and bones of their prey.
184
00:20:37,960 --> 00:20:43,240
And this, I can see,
has actually got vole skulls in it.
185
00:20:43,400 --> 00:20:48,240
But to discover exactly what
the state of the vole population is at the moment,
186
00:20:48,400 --> 00:20:55,640
I'll have to look inside the nest of a great grey owl,
and to do that I'll need this.
187
00:20:55,800 --> 00:21:03,480
All owls are fairly ferocious
and the great grey owl certainly can be,
188
00:21:03,640 --> 00:21:09,160
so as part of the standard equipment
of looking for owl nests you need this.
189
00:21:13,560 --> 00:21:17,960
Up there is one of their nests,
and the female has just flown off.
190
00:21:18,120 --> 00:21:22,200
She's perching in that tree over there,
keeping a very close eye on me.
191
00:21:22,360 --> 00:21:24,720
If I go up and have a look in the nest,
192
00:21:24,880 --> 00:21:30,560
I may be able to get some idea
as to how the vole cycle is going.
193
00:21:40,880 --> 00:21:45,240
And... come on...
194
00:21:45,400 --> 00:21:49,160
there is just one chick.
195
00:21:49,320 --> 00:21:53,240
If the voles had been
at the height of their population,
196
00:21:53,400 --> 00:21:57,760
there would probably be four chicks
in such a nest as this,
197
00:21:57,920 --> 00:22:01,200
but the fact there is only one
makes it pretty clear
198
00:22:01,360 --> 00:22:05,320
that the vole population
is already beginning to crash.
199
00:22:05,480 --> 00:22:15,040
So it is very likely the female and her mate
will soon be on their way back to Russia.
200
00:22:17,760 --> 00:22:21,880
There's now just a month left
of the short northern summer.
201
00:22:22,040 --> 00:22:25,080
Many of the birds that came up here
to harvest the insects and to breed
202
00:22:25,240 --> 00:22:30,680
will soon be moving back again
to avoid the severities of the coming winter.
203
00:22:30,840 --> 00:22:35,160
Some, like the redwing,
will go to open pastureland down south.
204
00:22:35,320 --> 00:22:38,080
The brambling prefers beech woodland,
205
00:22:38,240 --> 00:22:43,120
and will leave almost as soon as it has finished
its summer moult.
206
00:22:48,320 --> 00:22:51,040
The hawk owl is driven south by hunger,
207
00:22:51,200 --> 00:22:56,680
for as the forest gets colder,
there is less food to be found.
208
00:22:56,920 --> 00:23:00,960
As it flies south,
so the trees beneath change character.
209
00:23:01,120 --> 00:23:06,120
The ranks of dark conifers are replaced
by the brighter green of the broadleaved trees:
210
00:23:06,280 --> 00:23:10,760
Oak and ash, birch and beech.
211
00:23:35,520 --> 00:23:40,720
Down here, the weather's warmer, the summers
are longer, and the woodlands are free of frost,
212
00:23:40,880 --> 00:23:45,520
not for just two or three months in the year,
but for eight or nine,
213
00:23:45,680 --> 00:23:47,960
and the shape of the trees is very different.
214
00:23:48,120 --> 00:23:51,600
Instead of their branches drooping down,
and so shedding the snow,
215
00:23:51,760 --> 00:23:54,240
these branches spread out widely,
216
00:23:54,400 --> 00:23:59,280
carrying tier upon tier of leaves with which
to catch the abundant energy of the sun.
217
00:23:59,440 --> 00:24:01,520
And the leaves are very different.
218
00:24:01,680 --> 00:24:06,680
They are not covered with a thick, protective rind,
but are thin, delicate structures.
219
00:24:06,840 --> 00:24:10,040
During the summer water is more accessible,
220
00:24:10,200 --> 00:24:13,760
so there is less need
to take rigorous measures to conserve it.
221
00:24:13,920 --> 00:24:18,360
Indeed, during hot days
the trees evaporate large quantities to keep cool.
222
00:24:18,520 --> 00:24:21,400
So the pores through which they breathe
are numerous,
223
00:24:21,560 --> 00:24:25,000
and not in pits as they are in the pines.
224
00:24:27,600 --> 00:24:35,760
These succulent, soft leaves, unlike pine needles,
are relished as food by all kinds of creatures.
225
00:24:40,480 --> 00:24:42,520
Large animals, like deer, take many of them,
226
00:24:42,680 --> 00:24:48,200
but the greatest quantity by far
is gathered by insects.
227
00:25:12,640 --> 00:25:18,200
The forest canopy in late summer has more birds
in it than at any other time of the year.
228
00:25:18,640 --> 00:25:21,280
There are returning migrants
newly arrived from the north,
229
00:25:21,440 --> 00:25:25,320
resident breeders gathering food
to feed their second families of the season,
230
00:25:25,480 --> 00:25:28,560
and young fledglings
starting to forage for themselves
231
00:25:28,720 --> 00:25:32,040
and still not sure what is edible and what isn't.
232
00:25:32,200 --> 00:25:37,840
Nearly all of them are hunting for insects,
and the crop they take is huge.
233
00:25:49,880 --> 00:25:54,280
Not surprisingly, the insects have evolved
many ways of protecting themselves.
234
00:25:54,440 --> 00:25:58,640
They snip off half-eaten leaves so as to give
the minimum sign of their presence.
235
00:25:58,800 --> 00:26:02,680
They disguise themselves
as a blob of cuckoo spit or a bird dropping,
236
00:26:02,840 --> 00:26:07,160
but if they move, as eventually they must,
their concealment is lost.
237
00:26:18,280 --> 00:26:20,880
Some hang in places which are difficult to reach.
238
00:26:21,040 --> 00:26:28,040
This might baffle a fledgling, but an adult
great tit is both experienced and agile.
239
00:26:36,840 --> 00:26:41,520
The tree creeper
specialises in insects that live on bark.
240
00:26:44,240 --> 00:26:49,840
A poplar hawk moth tries to defend itself
by pretending to be fierce.
241
00:27:02,320 --> 00:27:05,640
The nuthatch habitually
works its way down the trunk,
242
00:27:05,800 --> 00:27:08,560
and that way may see insects
that have been overlooked
243
00:27:08,720 --> 00:27:12,240
by tree creepers that habitually come up it.
244
00:27:29,400 --> 00:27:31,600
One of the most expert of all bark-feeders,
245
00:27:31,760 --> 00:27:36,880
and in some ways the most specialised of all
the birds living in the tall trees of these forests,
246
00:27:37,040 --> 00:27:38,960
are the woodpeckers.
247
00:27:39,120 --> 00:27:42,000
The greater spotted woodpecker
is typical of them.
248
00:27:42,160 --> 00:27:44,400
Its hearing is excellent
and it locates the grubs it seeks
249
00:27:44,560 --> 00:27:50,320
by the tiny sounds they make
as they move inside the bark.
250
00:27:51,560 --> 00:27:56,040
Its tall feathers have strong quills
and serve as props for its body.
251
00:27:56,200 --> 00:28:03,800
Its bill has a resilient pad at the base which
cushions its brain from the shock of its drilling.
252
00:28:03,960 --> 00:28:11,600
Its feet give it a grip in all directions, with
two toes pointing forwards and two backwards.
253
00:28:11,760 --> 00:28:14,400
Each continent
has its own range of woodpeckers.
254
00:28:14,560 --> 00:28:15,920
Europe has ten species,
255
00:28:16,080 --> 00:28:20,160
but here in North America
there are over twice as many.
256
00:28:20,320 --> 00:28:25,400
This one, a sapsucker, drills holes in trees
not for insects, but for sap.
257
00:28:25,560 --> 00:28:29,000
It digs lines of these wells
in many kinds of trees.
258
00:28:29,160 --> 00:28:33,560
Each little hole points slightly downwards
so that the sap does not trickle out
259
00:28:33,720 --> 00:28:36,160
but collects in a small pool inside,
260
00:28:36,320 --> 00:28:38,960
and the sapsucker collects it with its tongue.
261
00:28:39,120 --> 00:28:41,440
And so do other birds.
262
00:28:45,160 --> 00:28:46,480
A hummingbird.
263
00:28:46,640 --> 00:28:49,880
Most of its family live in the tropics
and feed on nectar,
264
00:28:50,040 --> 00:28:56,480
but this one comes north in the summer
and finds tree sap just as acceptable.
265
00:28:56,640 --> 00:29:01,040
Flies, too, come to the sweet sap.
266
00:29:14,560 --> 00:29:19,800
In late summer, the parent sapsuckers
lead their fledglings to the wells
267
00:29:19,960 --> 00:29:25,920
and leave them to feast
not only on the sap but on the insects it attracts.
268
00:29:26,840 --> 00:29:33,080
This American woodpecker uses its drilling skills
to bore neat sockets in dead tree trunks.
269
00:29:33,240 --> 00:29:36,600
Acorns are its main food,
but during the season,
270
00:29:36,760 --> 00:29:40,440
there are far more acorns
than the woodpeckers can eat immediately.
271
00:29:40,600 --> 00:29:42,560
But they don't leave them for others.
272
00:29:42,720 --> 00:29:46,840
Several birds share a communal acorn treasury,
like this one.
273
00:29:47,000 --> 00:29:51,560
They hammer the acorns into the holes so firmly
that few other creatures can get them out,
274
00:29:51,720 --> 00:29:57,280
and the store will keep the acorn woodpeckers
supplied throughout the year.
275
00:30:02,200 --> 00:30:07,160
The ripening acorns herald the end of summer
and the beginning of autumn.
276
00:30:07,320 --> 00:30:10,800
Trees and bushes proffer their seeds
to the forest animals.
277
00:30:10,960 --> 00:30:13,640
Some are wrapped in soft and tasty flesh
278
00:30:13,800 --> 00:30:19,160
to tempt the animals to eat them
and so transport them to new sites.
279
00:30:19,320 --> 00:30:21,160
Others are packed with nourishment,
280
00:30:21,320 --> 00:30:24,840
not for animals, but to provide food
for the germinating seedling,
281
00:30:25,000 --> 00:30:27,280
but the animals eat them just the same.
282
00:30:27,440 --> 00:30:34,920
Even the hard and unpromising-looking acorns
of the American pin oak are collected by racoons.
283
00:30:43,200 --> 00:30:49,880
The squirrel's habit of burying acorns for a winter
store has been the start of many an oak.
284
00:30:50,040 --> 00:30:55,840
The black bear, on occasion,
will eat fish and voles and even carrion,
285
00:30:56,000 --> 00:30:58,720
but much of its diet is vegetable.
286
00:30:58,880 --> 00:31:01,160
It will dig for roots and even eat pine cones,
287
00:31:01,320 --> 00:31:07,000
but it has a very sweet tooth
and just now it relishes the fruit.
288
00:31:20,480 --> 00:31:24,040
All sorts of mammals are now clambering around
in the trees in search of fruit.
289
00:31:24,200 --> 00:31:27,640
The possum,
a strange primitive animal of the Americas
290
00:31:27,800 --> 00:31:33,280
related more closely to kangaroos than to rats,
eats almost anything.
291
00:31:35,320 --> 00:31:40,280
Few of them can get to the very tops of the trees
or the thinnest twig,
292
00:31:40,440 --> 00:31:43,360
but a chipmunk can.
293
00:31:45,760 --> 00:31:49,160
The chills of autumn
presage the coming of winter.
294
00:31:49,320 --> 00:31:53,040
The delicate leaves worked efficiently
throughout the warm moist summer,
295
00:31:53,200 --> 00:31:55,760
but they are not suited to cold weather.
296
00:31:55,920 --> 00:31:57,480
Frost will damage them.
297
00:31:57,640 --> 00:31:59,840
Their abundant pores would lose too much water.
298
00:32:00,000 --> 00:32:03,960
So the green chlorophyll in them is broken down
and withdrawn into the tree,
299
00:32:04,120 --> 00:32:07,080
revealing the red and brown waste products,
300
00:32:07,240 --> 00:32:10,040
and the leaves fall.
301
00:32:10,200 --> 00:32:13,640
And they, too, provide food
for another woodland community,
302
00:32:13,800 --> 00:32:18,360
the inhabitants of the leaf litter.
303
00:32:19,600 --> 00:32:24,560
There may be 100,000 box mites
in every cubic yard.
304
00:32:24,720 --> 00:32:26,880
And there are many other creatures too,
305
00:32:27,040 --> 00:32:29,360
chewing their way through the dead leaves,
306
00:32:29,520 --> 00:32:31,680
extracting what nutriment they can
307
00:32:31,840 --> 00:32:36,720
and leaving the remainder
to be dealt with by fungi and bacteria.
308
00:32:42,840 --> 00:32:45,400
They themselves are hunted
by monsters in miniature,
309
00:32:45,560 --> 00:32:47,280
pseudoscorpions,
310
00:32:47,440 --> 00:32:53,280
horrific in close-up, but,
perhaps fortunately, the size of a pinhead.
311
00:33:28,040 --> 00:33:33,200
Snails are giants in comparison and,
since they carry their shells around with them,
312
00:33:33,360 --> 00:33:38,640
they might seem to be fairly well protected
against any creatures smaller than a bird.
313
00:33:38,800 --> 00:33:44,240
But one particular beetle
has specialised equipment for dealing with them.
314
00:33:45,320 --> 00:33:48,120
Its head and jaws are long and thin.
315
00:34:15,160 --> 00:34:18,040
Almost hidden in the leaves
of these American woods
316
00:34:18,200 --> 00:34:23,160
are some spectacularly coloured
little creatures hardly bigger than worms.
317
00:34:26,280 --> 00:34:29,360
They are amphibians: Salamanders.
318
00:34:29,520 --> 00:34:35,040
Almost every mountain range in the US
has its own species with its own colours,
319
00:34:35,200 --> 00:34:38,400
but, being nocturnal, they're rarely seen.
320
00:34:58,680 --> 00:35:03,280
Shrews eat most small living things they
come across, and they are formidable hunters,
321
00:35:03,440 --> 00:35:08,040
for they are one of the few mammals
that has a poisonous bite.
322
00:35:13,080 --> 00:35:18,320
The salamander's only defence is
to produce an acrid liquid from glands on its tail.
323
00:35:18,480 --> 00:35:23,040
The first time a shrew encounters this, it usually
takes no notice and eats the salamander,
324
00:35:23,200 --> 00:35:25,600
but apparently the taste is not very nice,
325
00:35:25,760 --> 00:35:28,520
for on later encounters, like this one,
326
00:35:28,680 --> 00:35:31,520
one sniff reminds the shrew
the meal won't be a good one
327
00:35:31,680 --> 00:35:35,200
and it leaves the salamander alone.
328
00:35:40,480 --> 00:35:43,320
The summer visitors have departed.
329
00:35:43,480 --> 00:35:45,720
The woods have fallen silent.
330
00:35:45,880 --> 00:35:49,800
The days are shortening
and the temperature falling.
331
00:36:19,720 --> 00:36:24,720
Eventually the land is gripped tight by frost.
332
00:36:49,720 --> 00:36:51,200
It's late winter.
333
00:36:51,360 --> 00:36:54,680
The once-resplendent trees
are now mere skeletons
334
00:36:54,840 --> 00:36:59,240
and life in these woodlands
has come almost to a standstill.
335
00:36:59,400 --> 00:37:02,160
The trees, without their leaves, can't grow.
336
00:37:02,320 --> 00:37:07,160
The birds that came visiting up here
during the summer have now retreated south,
337
00:37:07,320 --> 00:37:12,600
and some of these small mammals
have crawled into holes and gone to sleep.
338
00:37:12,760 --> 00:37:17,680
Their heartbeat has almost stopped,
their bodies have become as cold as stone.
339
00:37:17,840 --> 00:37:19,880
They're hibernating.
340
00:37:20,040 --> 00:37:23,280
But that sleep doesn't last throughout the winter.
341
00:37:23,440 --> 00:37:27,160
They wake up every four or five days
and go and look for food.
342
00:37:27,320 --> 00:37:30,880
Like, for example,
those small chipmunks over there.
343
00:37:31,040 --> 00:37:34,640
Not only warmth but intense cold
will bring them out,
344
00:37:34,800 --> 00:37:37,840
for although their body temperature falls
while they hibernate,
345
00:37:38,000 --> 00:37:40,680
if it drops to freezing point, they will die.
346
00:37:40,840 --> 00:37:44,800
So in really cold spells, they must get up
and warm themselves with a little exercise,
347
00:37:44,960 --> 00:37:49,440
even though it dangerously depletes
their fat reserves.
348
00:37:49,800 --> 00:37:53,440
But in these American woodlands
there is one spectacular sleeper
349
00:37:53,600 --> 00:37:55,760
who dozes for months on end.
350
00:37:57,200 --> 00:37:59,240
Just look at this.
351
00:38:05,800 --> 00:38:07,360
A black bear.
352
00:38:09,240 --> 00:38:13,840
She retired to this den in early autumn,
and after a month or so of drowsiness,
353
00:38:14,000 --> 00:38:17,960
produced her cubs.
354
00:38:18,120 --> 00:38:19,840
In the colder northern parts of these woods,
she may spend six or seven months here,
355
00:38:20,000 --> 00:38:21,840
during which time she suckles her cubs
356
00:38:22,000 --> 00:38:26,000
but neither feeds herself
nor urinates nor defecates.
357
00:38:26,160 --> 00:38:30,600
So she spends the majority of her life
half-asleep.
358
00:38:32,360 --> 00:38:37,920
When spring at last comes, the brown carpet
of rotting leaves is suddenly flooded with colour.
359
00:38:40,920 --> 00:38:44,800
The plants that live close to the ground
now make haste to sprout and flower
360
00:38:44,960 --> 00:38:47,040
and soak up the spring sunshine
361
00:38:47,200 --> 00:38:52,640
before the trees above
produce their own leaves and cut out the light.
362
00:38:54,960 --> 00:38:57,320
The bear's den is empty,
363
00:38:57,480 --> 00:39:00,840
but the owners haven't gone far.
364
00:39:09,520 --> 00:39:12,040
There's still not much to eat, only a few leaves,
365
00:39:12,200 --> 00:39:16,360
nor will there be until the first of the berries
come into fruit in summer,
366
00:39:16,520 --> 00:39:20,120
but meanwhile at least the sun is warm.
367
00:39:25,120 --> 00:39:27,920
Another mother spends the spring up in a tree:
368
00:39:28,080 --> 00:39:31,880
A wood duck, only she is about to leave.
369
00:39:37,720 --> 00:39:40,280
The hole has provided a secure nest,
370
00:39:40,440 --> 00:39:45,040
but all ducklings follow their mothers
as soon as they hatch.
371
00:40:15,320 --> 00:40:20,160
And now new forms appear
from among the dead leaves.
372
00:40:55,240 --> 00:40:57,280
The spring showers soak the woodlands
373
00:40:57,440 --> 00:41:01,320
and create just the moist, warm conditions
needed by the fungi
374
00:41:01,480 --> 00:41:04,040
to produce their fruiting bodies.
375
00:41:04,200 --> 00:41:07,960
These must be mature
and ready to discharge their microscopic spores
376
00:41:08,120 --> 00:41:11,240
by the time the dry winds of summer
begin to blow,
377
00:41:11,400 --> 00:41:16,360
so that their spores, like dust,
will be carried all through the forest.
378
00:41:17,920 --> 00:41:21,800
Once, the woods of North America
stretched over the eastern half of the continent
379
00:41:21,960 --> 00:41:26,440
in an almost continuous band
hundreds of miles deep.
380
00:41:26,600 --> 00:41:30,800
Today, the majority has been felled
to make space for farmland and cities,
381
00:41:30,960 --> 00:41:34,720
but enough remains
to make plain their splendour.
382
00:41:37,800 --> 00:41:40,280
And now we've come farther south still.
383
00:41:40,440 --> 00:41:44,320
I'm on the borders of Florida and Georgia
in the southern United States,
384
00:41:44,480 --> 00:41:48,600
and here it's very hot in the summer
and the winters are very mild,
385
00:41:48,760 --> 00:41:51,600
with only a few frosts,
and none of them severe.
386
00:41:51,760 --> 00:41:58,120
So some of the broadleaved trees here, like
this oak, don't shed all their leaves in the autumn
387
00:41:58,280 --> 00:42:02,080
but keep them throughout the year
and continue growing.
388
00:42:02,240 --> 00:42:06,080
And these aren't the only evergreens
that are here, either.
389
00:42:06,240 --> 00:42:08,360
There are pines.
390
00:42:08,520 --> 00:42:13,360
In some parts where the soil is very rocky
or sandy and poor in nutrients,
391
00:42:13,520 --> 00:42:16,920
the pines will grow
because nothing else can survive there.
392
00:42:17,080 --> 00:42:21,600
But this pine forest owes its existence
to another factor altogether.
393
00:42:32,000 --> 00:42:35,520
Oak saplings are killed within minutes by fire.
394
00:42:38,160 --> 00:42:42,720
But the terminal buds of young pines
are surrounded by a shock of needles.
395
00:42:42,880 --> 00:42:48,000
They burn at a relatively low temperature,
and by the time the flames have consumed them,
396
00:42:48,160 --> 00:42:50,320
the main fire has swept by
397
00:42:50,480 --> 00:42:57,640
and the bud at the top of the stem, from which
new growth will come, is still unharmed.
398
00:42:57,960 --> 00:43:03,960
Fires like these are not just the work
of careless people, they occur naturally.
399
00:43:04,120 --> 00:43:08,080
The spark that regularly sets fire to these forests
is lightning.
400
00:43:08,240 --> 00:43:11,920
In this part of the southern States,
violent thunderstorms are common
401
00:43:12,080 --> 00:43:14,360
and lightning often strikes the taller trees,
402
00:43:14,520 --> 00:43:20,360
scoring a deep groove down the length
of the trunk as it flashes down to earth.
403
00:43:22,080 --> 00:43:26,760
And this at my feet
is the tinder which set it aflame.
404
00:43:26,920 --> 00:43:32,240
These are pine needles,
and they're so full of resin and they're so dry
405
00:43:32,400 --> 00:43:34,920
that they flame up very easily.
406
00:43:35,080 --> 00:43:38,800
But the fire they produce is not very hot,
and it's also very short-lived,
407
00:43:38,960 --> 00:43:43,240
so that if any creature can survive fire
for just one or two minutes,
408
00:43:43,400 --> 00:43:46,960
then it can survive a fire like this.
409
00:43:49,480 --> 00:43:52,440
The rattlesnake,
like many other ground-living animals,
410
00:43:52,600 --> 00:43:55,960
regularly takes refuge
from the midday sun in holes,
411
00:43:56,120 --> 00:44:01,040
so now it knows exactly
where to go to escape the fire.
412
00:44:16,800 --> 00:44:20,320
But this hole is already occupied
by its digger and owner,
413
00:44:23,920 --> 00:44:26,680
a gopher tortoise.
414
00:44:40,800 --> 00:44:45,000
Rattlesnake and tortoise do not normally
interfere with one another...
415
00:44:58,000 --> 00:45:02,400
...and that seems to be the way
things are going to stay.
416
00:45:03,760 --> 00:45:07,680
But in the back of the burrow
lies another refugee, an indigo snake,
417
00:45:07,840 --> 00:45:11,240
and it, on occasion, eats rattlesnakes.
418
00:45:32,600 --> 00:45:37,960
But the fire is passing
and the rattlesnake can return to the forest.
419
00:45:43,400 --> 00:45:46,720
Some insects don't avoid fire,
they actively seek it.
420
00:45:46,880 --> 00:45:50,400
Beetles find it difficult to lay their eggs
in the pines
421
00:45:50,560 --> 00:45:52,760
because the trees swamp them with resin.
422
00:45:52,920 --> 00:45:56,000
But a tree killed by fire can't resist,
423
00:45:56,160 --> 00:45:59,200
and these beetles
take advantage of the situation.
424
00:45:59,360 --> 00:46:03,560
They have pits behind their legs
which are sensitive to infra-red rays,
425
00:46:03,720 --> 00:46:06,760
and therefore they can detect
the slightest rise in temperature,
426
00:46:06,920 --> 00:46:10,080
and with these to guide them, they travel
from all over the forest to the wake of the fire
427
00:46:10,240 --> 00:46:12,800
and arrive in hundreds.
428
00:46:15,880 --> 00:46:18,560
Quickly they mate.
429
00:46:23,840 --> 00:46:27,080
The females crawl all over the scorched trunks,
430
00:46:27,240 --> 00:46:30,760
seeking crevices in the bark
into which they can lay their eggs,
431
00:46:30,920 --> 00:46:36,160
so ensuring that their grubs
will have some nice nutritious bark to chew.
432
00:46:37,560 --> 00:46:39,680
As insects assemble in the burnt forest,
433
00:46:39,840 --> 00:46:42,320
the insect-eaters follow.
434
00:46:42,480 --> 00:46:47,440
The oak toad almost exactly matches the colour
of the charred forest floor.
435
00:46:48,960 --> 00:46:53,120
Other more conspicuous hunters
wait on newly emerged shoots.
436
00:46:58,360 --> 00:47:02,520
Within a couple of months of a summer fire,
the forest has more than recovered,
437
00:47:02,680 --> 00:47:04,480
it is rejuvenated.
438
00:47:04,640 --> 00:47:08,040
The fire has cleared away
the old growth on the ground,
439
00:47:08,200 --> 00:47:13,000
and by reducing the pine needles to ash
has released their nutrients into the soil,
440
00:47:13,160 --> 00:47:18,080
and now the ground sprouts more flowers
than at any other time.
441
00:47:29,520 --> 00:47:33,840
Because of regular fires,
big bushes can't establish themselves here,
442
00:47:34,000 --> 00:47:39,360
so swampy areas are not colonised
and sucked dry by them as happens elsewhere,
443
00:47:39,520 --> 00:47:42,720
and open marshes remain
where pitcher plants can grow
444
00:47:42,880 --> 00:47:45,520
and where frogs can swim and breed.
445
00:47:45,680 --> 00:47:52,920
Indeed, one species of frog lives nowhere else
but in these pools in the American pine barrens.
446
00:48:08,440 --> 00:48:13,120
The woodpeckers here can't excavate their nest
in dead trees as do woodpeckers elsewhere,
447
00:48:13,280 --> 00:48:17,160
for in this fire-ravaged forest
they would risk incineration,
448
00:48:17,320 --> 00:48:21,760
so the red-cockaded woodpecker
drills its holes in living pines.
449
00:48:21,920 --> 00:48:27,720
But the wood is so hard, it takes several
woodpeckers about two years to dig the hole.
450
00:48:29,560 --> 00:48:35,240
Resinous sap seeps out around the hole where
the outer layers of the tree have been breached.
451
00:48:35,400 --> 00:48:38,800
So the birds make their hole
low down on the trunk
452
00:48:38,960 --> 00:48:44,280
where the inner sap-free heartwood
is thick enough to accommodate the entire nest.
453
00:48:44,520 --> 00:48:46,600
The flow of resin is diverted to the outside
454
00:48:46,760 --> 00:48:51,240
by drilling pits like sap wells
above and below the hole.
455
00:48:56,560 --> 00:49:04,280
It's in these laboriously excavated holes that
the red-cockaded woodpecker raises its young.
456
00:49:10,520 --> 00:49:15,440
The holes are very conspicuous, for each is
surrounded by a sheet of yellow congealed resin.
457
00:49:18,640 --> 00:49:24,040
The rat snake is a great robber of nests
and stealer of chicks.
458
00:49:37,760 --> 00:49:40,480
It's an extremely skilful tree climber.
459
00:49:40,640 --> 00:49:45,440
Since the woodpecker's hole in the living tree
has to be fairly low down on the trunk,
460
00:49:45,600 --> 00:49:52,040
it is within easy reach of the snake and therefore
might seem to be in considerable danger.
461
00:49:52,200 --> 00:49:54,680
But now the other function of all that resin,
462
00:49:54,840 --> 00:49:57,600
deliberately produced around the nest
by the woodpecker,
463
00:49:57,760 --> 00:49:59,720
is about to become clear.
464
00:50:28,120 --> 00:50:32,240
The chemicals in the resin
seem to irritate the snake beyond endurance,
465
00:50:32,400 --> 00:50:35,760
and it arches its body away.
466
00:50:37,760 --> 00:50:41,080
Eventually it's too much.
467
00:50:43,600 --> 00:50:48,600
So fire, one way or another, influences
the whole community of animals and plants
468
00:50:48,760 --> 00:50:51,640
in the pine forests of the south.
469
00:50:52,000 --> 00:50:57,800
This injury was also caused by fire,
and this is also a coniferous tree,
470
00:50:57,960 --> 00:51:00,920
but a very different one.
471
00:51:01,080 --> 00:51:10,600
To start with, it's over 40 feet across
along its base and it's 267 1/2 feet high.
472
00:51:11,120 --> 00:51:14,720
This is a giant sequoia.
473
00:51:15,640 --> 00:51:19,640
It's thought to be about 2,500 years old,
474
00:51:19,800 --> 00:51:26,520
but the largest individual tree of all is this one,
known as the General Sherman.
475
00:51:26,680 --> 00:51:32,920
It's just taller
and it's estimated to weigh 1,385 tons,
476
00:51:33,080 --> 00:51:38,240
which makes it the most massive
living organism in the world.
477
00:51:39,680 --> 00:51:43,600
Although these trees are growing
almost as far south as the southern pines,
478
00:51:43,760 --> 00:51:48,200
the climate here, 2,000 metres up
in the Sierra Nevada mountains,
479
00:51:48,360 --> 00:51:52,880
is much colder and snow lies on the ground
for almost half the year.
480
00:51:53,040 --> 00:51:55,560
It's as though, by climbing to this height,
481
00:51:55,720 --> 00:51:59,040
we have returned climatically
to the great forests of the north.
482
00:51:59,200 --> 00:52:03,120
During the Ice Age,
these sequoias grew over much of North America.
483
00:52:03,280 --> 00:52:06,680
But when, some 8,000 years ago,
the earth began to warm,
484
00:52:06,840 --> 00:52:13,120
they died out except for these isolated groups
high up in the mountains.
485
00:52:20,320 --> 00:52:23,280
We've travelled some 2,000 miles southwards
486
00:52:23,440 --> 00:52:27,520
since we started at the tree line
near the Arctic Circle,
487
00:52:27,680 --> 00:52:33,440
and in all that vast territory the majority
of the forest trees have been conifers,
488
00:52:33,600 --> 00:52:40,040
so it seems only right and proper that
we should end with these, the noblest of them all.
489
00:52:40,200 --> 00:52:43,640
As a group,
the conifers owe much of their success
490
00:52:43,800 --> 00:52:48,040
to their ability to cope
with the changeable northern climate.
491
00:52:48,200 --> 00:52:52,800
They can survive both the short, dark days
of winter with their bitter cold,
492
00:52:52,960 --> 00:52:57,560
as well as the long sunny days of summer
with their raging fires.
493
00:52:57,720 --> 00:53:02,200
But if we continue a further 1,000 miles
southwards, we come to the tropics,
494
00:53:02,360 --> 00:53:05,840
and there the climate is radically different.
495
00:53:06,000 --> 00:53:08,880
It's no longer very variable
but remarkably constant,
496
00:53:09,040 --> 00:53:14,680
with much the same amounts of light
and rain and heat throughout the year.
497
00:53:14,840 --> 00:53:20,280
There the other great group of forest trees,
the broadleaved trees, come into their own.
498
00:53:20,440 --> 00:53:25,720
That is the jungle,
and that's where we'll be in the next programme.
499
00:53:25,770 --> 00:53:30,320
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